If you have made lots of changes to your site, you can resubmit your sitemap if you would like. It is important not to do this very often though as Google might look at this as spam.
The best way to get Google to come to your site and keep fresh copies of your site pages in its index is to add to your site often.
A great way to continually add new content, thus training the search engines to come often, is with blogging. For more information on this please see our tutorial: Using the Tumblr Widget.
Here is how to resubmit your sitemap in your Google Webmaster account:
1. Sign in to your Google Webmaster account.
2. Click on the URL link of the site you want to resubmit a sitemap for.
3. In the Sitemaps section click on the link that says More.
4. Click Resubmit Sitemap.